The present invention relates to a process or method for obtaining a pure hydrocarbon from a sump product of an extractive distillation.
An extractive distillation using an N-substituted morpholine, whose substituents do not contain more than seven carbon atoms, as selective solvent is known, in which the sump product is fed into a center portion of a distillation separator column. The hydrocarbon materials are distilled off the top of the distillation separator column, while the solvent is drawn off from the sump of the distillation separator column and after an appropriate cooling is returned to the extractive distillation column.
Extractive distillation of hydrocarbon-containing starting materials using the above-mentioned N-substituted morpholine, particularly N-formyl morpholine, as selective solvent, has been known for a long time and is currently used as a large-scale industrial process for obtaining highly pure aromatic hydrocarbons. The process has been used to obtain other types of hydrocarbon substances, e.g. olefins and diolefins. The major portion of the solvent in the sump of the extractive distillation column is enriched with the hydrocarbons obtained from the appropriate entry product and the hydrocarbons must be separated in a downstream distillation separator column. The hydrocarbons to be obtained are distilled off the top of the distillation separator column, while the solvent is obtained as a sump product and is fed back to the extractive distillation column. The distillation separator column has a side boiler for heating as well as the conventional sump boiler, which vaporizes the reflux coming from the distillation separator column.
In performing the above-described process one understandably tries to obtain as complete a separation of the hydrocarbons as possible from the solvent in the distillation separator column to obtain them with a minimum loss. In the currently practiced methods of this kind however this could only be achieved by operation of the sump at a temperature which was so high that high pressure steam was required for column heating, while for heating of the extractive distillation column normally low pressure steam was sufficient. An additional disadvantage of operation with comparatively high temperature in the separator column is that there is an increased tendency for thermal decomposition of the solvent because of the comparatively high temperature in the distillation separator column.